Field programmable gate arrays are a type of programmable logic device, having a programmable array of logic modules. Each logic module is comprised of at least one logic gate. These logic modules are interconnected with a matrix of conductive lines, which intersect at crosspoints that may be selectively made conductive or nonconductive during a programming process. For example, if a connection is not wanted at a certain crosspoint, a fuse at the crosspoint is blown. By programming the interconnections among the logic cells, the gate array is made to realize a desired logical function.
A recent development in programmable gate arrays is the use of anti-fuses instead of fuses at the crosspoints. The devices are programmed by applying a voltage to close electrical connections. Usually, the voltages used for the programming inputs are high in relation to the voltage required for operation after programming.
A problem with programming anti-fuses of gate arrays is that the higher programming voltage inputs must be isolated from the lower voltage circuits of the logic portions of the gate array. One approach to achieving such isolation is to interpose isolation transistors between each logic module and its associated anti-fuses. These isolation transistors are usually large and thus require extra space on the chip.